1. Field of the Invention
The present invention is generally in the field of fabrication of semiconductor structures. More particularly, the invention is in the field of fabrication of semiconductor on insulator (SOI) structures.
2. Background Art
Semiconductor devices and structures are typically fabricated on conventional semiconductor wafers. One type of conventional semiconductor wafer is a bulk silicon wafer, which has a substantially uniform composition and is relatively inexpensive. Circuits made by fabricating semiconductor structures such as, for example, transistors, on conventional bulk silicon wafers typically suffer from several drawbacks. For example, it is difficult to electrically isolate such semiconductor structures when fabricated on a bulk silicon wafer, because although the structures can be partially electrically isolated by virtue of, for example, isolating trenches, electric currents can still flow under such trenches. Neighboring semiconductor devices in such structures thus tend to interfere with one another when fabricated on bulk silicon wafers.
Some of the problems experienced when utilizing bulk silicon wafers can be partially avoided by instead using another conventional semiconductor wafer, such as a semiconductor on insulator (“SOI”) wafer (for example, a silicon on insulator wafer). Instead of having a substantially uniform composition like a conventional bulk silicon wafer, a SOI wafer has several layers, such as a device layer, a buried oxide layer, and a bulk semiconductor layer. The utilization of a buried oxide layer can help address the electrical isolation problem experienced when utilizing bulk silicon wafers. The buried oxide layer, utilized in concert with semiconductor structures incorporating isolating trenches, can more effectively isolate semiconductor devices fabricated in the device layer. Disadvantageously, semiconductor devices must typically be redesigned for fabrication in the device layer of a conventional SOI wafer. Moreover, bulk silicon wafer design methodologies and design models (some times also referred to as “design kits”) must be re-developed for use in conventional SOI wafer design, because a conventional SOI wafer has electrical and other characteristics that significantly differ from those of a bulk silicon wafer.
Thus, there is a need in the art for a semiconductor structure that overcomes the disadvantages associated with utilizing conventional semiconductor structures and conventional SOI structures in semiconductor device fabrication.